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At 8am on Sunday morning the streets of Turin were deathly quiet. The residents, it seemed, were lost to slumber.

And yet there was a visible police presence. The last time I'd seen this many carabinieri was in Naples during a home game.

By the time I left Biratti & Milano, a splendid art nouveau coffee shop in one of Turin's historic arcades, locals were beginning to dribble into churches for mass. I crossed the piazzas linking the city's meticulous grid to the accompaniment of melodious bells, pausing at the lantern-domed Church of San Lorenzo.

The baroque church was brimming with worshippers. In the late 16th century the Chiesa di San Lorenzo was the first seat of the famous Shroud of Turin; a temporary home until the Chapel of the Holy Shroud (Cappella della Sacra Sindone) was built and the world's most controversial piece of cloth moved to the cathedral around the corner.

Worshippers in Turin (Photo: Getty)

And there it has remained. But it doesn't get out much. Officially once every 25 years - unless there happens to be a Jubilee (2000), an anniversary (400 years since its arrival, in 1978) or a fire (1997).

(The restored 14-foot relic did go on display briefly in April 2010. Our guide, an atheist, said the mayor foresaw the economic slump and took the opportunity to put some more money in the local pockets - the guides, the hotels and the restaurants are all busy when pilgrims come.)

According to shroud.com, during its last public exposition in 1998 two million pilgrims saw the shroud over a two-month period. At least half that number are expected to see it this time around.

Examining the relic (Photo: Getty)

So why is it out now?

Officially, it is revealing itself on account of St John Bosco, who was born 200 years ago in August.

Heightened security is in place in the city (Photo: Getty)

Our guide thought the heightened security was due to Isis (it doesn't get more Christian than the Holy Shroud); others said it was a trial run for the Papal visit. The Pope will make a pilgrimage to Turin by on June 21 to venerate the shroud.

Approaching Piazza San Giovanni, by the Cathedral of St John the Baptist, I saw a riot van, a shroud pop-up shop and an autopompa (fire engine). In front of the cathedral a crowd of happy-clappy French pilgrims seemed jubilant. "Gloria!" they sang, while performing a backwards version of the Mexican wave, from their waists to the ground.

Queues outside the cathedral (Photo: Getty)

On the steps of the cathedral were more police, including one wearing a cape with a flash of red on the left shoulder.

My fleeting visit to the city meant I didn't get the chance to see the exhibition, but in Liguria the next day, I met Adrian Everitt, a freelance tour manager for Great Rail Journeys. He had just taken 22 visitors on the 800-metre trail from the city's Opera House via the Royal Gardens to the cathedral and the main altar where the shroud will sit in a temperature-controlled, bullet-proof display case until June 24.

The shroud in its temperature-controlled, bullet-proof display case (Photo: Getty)

"It was all very efficient," he said, "with a metal scanner. A bit like going on Eurostar."

And the shroud?

"They all said they were glad to have seen it," he said of his 22 passengers. "But maybe it's easier to connect more with the Mona Lisa."

The Shroud Public Exhibition runs until June 24. Visits are free but booking is essential (sindone.org). The next public viewing is scheduled for 2025. Great Rail Journeys is including Shroud Tours on its Liguria rail trips.